1. Field of the Invention
The present invention relates to a technique for reducing vibration in a power impact tool that linearly drives a tool bit in its longitudinal direction by a swinging mechanism
2. Description of the Related Art
A technique for reducing or alleviating vibration caused in an electric hammer drill with a swinging mechanism is disclosed in EP1000712. According to the known art, the swinging mechanism includes a swinging ring swinging in the axial direction of a rotating shaft by rotation of the rotating shaft driven by a motor. A tool bit is linearly driven by a tool driving mechanism connected to an upper end region of the swinging ring. In a vibration reducing mechanism in this known technique, a counter weight is connected to the lower end region in a position shifted about 180° in the circumferential direction from the connection between the swinging ring and the tool driving mechanism. The counter weight linearly moves by the swinging movement of the swinging ring and thereby reduces vibration caused during the operation.
The counter weight is disposed in a lower region apart from the swinging ring. Therefore, the vertical distance between the path of travel of the counter weight and the axis of the hammer bit is widened. As a result, when the tool driving mechanism and the counter weight are driven by the swinging ring, unnecessary vibration is caused by a couple around the horizontal axis that intersects with the axis of the rotating shaft. Further, because the counter weight linearly moves by the swinging movement of the swinging ring, loss of a striking energy of the tool bit may be caused by resistance of the sliding area.